Machines such as road cutting recycler/reclaimers or planers, mining cutters, stabilizers, pulverizers, recyclers and other rotary cutters employ cutting bits mounted on a rotor which is rotated while the bits engage a material to be cut. The machines described, particularly those used for cutting hard materials such as asphalt, concrete, minerals and rock, are engineered to withstand the severe forces and abrasion inherent in engaging the material being cut. For example, in a road planer designed to remove an upper layer of asphalt or other road paving material from a road surface, a rotor supporting cutting bits is rotated by an engine and lowered to engage the road surface. Due to high abrasion, the cutting bits, bit holders and attachment parts on the rotor are worn or damaged, and thereby often fail, necessitating the replacement of the parts.
In some cutting machines in the prior art, the bit holders, also known as sockets, that hold the cutting bits are permanently affixed to a rotor, such as a drum or disk, by welding. In other cutting machines, the sockets are welded to blocks or spacers which are in turn welded to the rotor. Replacement of such sockets requires cutting off the old socket, grinding and cleaning the surface of the rotor, blocks or spacers, and accurately positioning the new socket and welding it in place. Such an operation is not only very time consuming, but occasionally also requires removal of the rotor assembly from the machine and transportation of the assembly to a shop to perform the work. Thus, the cost of replacement of the cutting bits is very expensive, and the downtime of the machine and resultant work delays are also very costly.
In some cases, the sockets are attached to bases which are bolted to the rotor. Attachment of the bases with conventional bolts presents various problems. For instance, the nut holding the bolt often will freeze on the bolt due to rust, or the bolt head will wear out or become stripped or sheared off. The bolts are subjected to heat caused by friction and stress, causing some bolts to bend or break. Removing a damaged bolt can be a tedious and time consuming procedure which often requires cutting the bolt with a welding torch. Because of the difficulties associated with the removal of the damaged parts of such bit attaching assemblies, the parts are often left on the rotor, where they can cause additional damage. Bolt-on and other replaceable sockets, or holders, are available, but most of them are very expensive, and their usage may not be justified due to high cost. Also, such designs still require an enormous amount of time to change the damaged sockets.
Sockets break or wear out frequently, so that repeated removal and replacement are necessary at each socket location on the rotor. The repeated welding necessary at each location crystallizes the material on the rotors, blocks or spacers, and, as a result, subsequent weldings have less and less strength and the welds repeatedly break. Another problem posed by such cutting and welding is that, without great care, the replacement sockets may not be positioned at the original locations and at the original angles. If a base and its corresponding socket are out of alignment on the cutting rotor when it is in use, the associated cutting bit will be subjected to different forces from the other cutting bits, which results in uneven wear among the bit attaching assemblies. A further problem often encountered with replacement bit attaching assemblies is an imprecise fit among the components of the assemblies. If the assemblies of sockets and bases are not solidly secured and tight fitting, the parts tend to break more frequently or wear at an accelerated rate due to the hammering or chattering of component on component.
In some cutting applications, it has been found that different numbers of cutting bits or teeth are desired to achieve greatest efficiency. For example, it may be desirable to remove asphalt from only a portion of a road surface. It is also desirable to be able to easily adjust the depth of the cut. These adjustments are typically achieved by removing a number of the cutting teeth from the rotor or replacing the entire rotor with a new rotor with an arrangement suited for the particular application. However, because of the cost, time and trouble involved in adding or removing the cutting bits or locating a suitable replacement rotor, contractors use an inefficient rotor or cutting bit arrangement for a job.